The nucleotide sequences of cDNA's for the evolutionarily diverged but highly conserved basal H2A isoprotein, H2A.Z, have been determined for the rat, cow, and human. Each of the cDNA isolates encodes the entire H2A.Z polypeptide. The human isolate is about 1.0 kilobase long. It contains a coding region of 387 nucleotides flanked by 106 nucleotides of 5' untranslated region (5'UTR) and 376 nucleotides of 3' untranslated region (3'UTR), which contains a polyadenylation signal followed by a poly A tail. The bovine and rat cDNA's have 97 and 94% nucleotide positional identity to the human cDNA in the coding region and 98% in the proximal 376 nucleotides of the 3'UTR which includes a polyadenylation signal. A potential stem-forming sequence imbedded in a direct repeat is found centered at 261 nucleotides into the 3'UTR. Each of the cDNA clones could be transcribed and translated to yield H2A.Z protein. A human genomic library in lambda has been screened with the human H2A.Z cDNA and the genomic form of the H2A.Z gene has been isolated. The 5' half of the gene contains at least two introns. We are utilizing exon- and intron-specific H2A.Z DNA to probe restriction enzyme cleaved human genomic DNA in order to be able to determine the copy number of the functional H2A.Z gene as well as the presence or absence of processed pseudogenes. Sequences upstream and downstream from the H2A.Z gene are being determined and the regulatory elements will be studied. The human genomic-lambda library has also been screened with the cDNA complement of a chicken major H2A variant gene and clones of the human H2A.l gene have been isolated and partially sequenced. This gene has been used to isolate plasmid clones from a human cDNA library which are likely to be representative of the gene for another minor histone variant, H2A.X.